A cylindrical ball bearing cage known from JP 2008 133 894 A has rolling element pockets which have the basic shape of a rectangle, the corners of which are expanded by rounded regions. The rounding of the corners is intended to reduce mechanical stresses.
A ball bearing cage known from DE 10 2004 018 868 A1 has substantially cylindrical rolling element pockets, which are enlarged by four grooves which extend in the radial direction of the ball bearing cage and which modify the cylindrical basic shape of each rolling element pocket in a square pattern.
Another ball bearing cage which has rolling element pockets that combine geometrical features of cylindrical openings with rectangular basic shapes is known from JP 2007 170 470 A, for example.